Method for dimensioning a mobile telecommunications network

ABSTRACT

A method for assessing the characteristics obtainable in a network for mobile telecommunications apparatuses suitable for managing calls with both data traffic and/or voice and data traffic. On the basis of the performance requested for the quantity and characteristics of the traffic required, the method provides a simple manner for determining both the effective performance of the network in terms of the probability of occupation of the radio channels and the probability of dropped calls during the peak traffic period and optimal dimensioning of the network.

TECHNICAL FIELD

This invention refers to a method for assessing the characteristics of anetwork for mobile telecommunications apparatuses on the basis ofparameters such as the number of radio resources (base stations)available and the amount of telephone traffic offered to it.

In particular, this invention relates to a method for assessing thecharacteristics in terms of dimensioning and performance of basestations of a GSM-GPRS type network (Global System for Mobilecommunications—General Packet Radio Service on mobile networks) which,as is known, uses a hybrid radio interface based on Frequency DivisionMultiple Access (FDMA) and Time Division Multiple Access (TDMA), andwhich makes it possible to manage both voice calls and data calls.

The method therefore is concerned with the assessment of the correctdimensioning and performance of radio resources on the basis of thenumber and duration of the voice telephone calls (voice traffic) and thenumber of and volume of information to transmit in data calls (datatraffic) and of the priority attributed to voice traffic calls comparedwith data traffic ones.

The method, in particular, concerns the determination of deathprobability of data calls associated to a determined status orconfiguration of the network.

BACKGROUND ART

Networks for mobile telecommunications apparatuses are known.

These networks are generally described as cellular and they aredistinguished by a plurality of cells, each defined as the group ofterritorial points served by the radio-electric signal radiated by anantenna (radio interface).

Apart from the intrinsic mobility of users, the main peculiarity ofnetworks of mobile apparatuses is the use of the radio interface asaccess port to the network itself.

It is also known that dimensioning and performance assessments oftelecommunications networks or systems in which the offered traffic iscomposed of voice and data traffics, can be evaluated by using themethod described in WO 02/080602. The known method is based on anM/M/N/Q model in which the system servers correspond to the cell trafficslots and the status of the cell is represented by the number of GPRSusers in the system; this model takes into account:

-   -   a queue of infinite length (Q=∞) on the basis that, in the case        of congestion of the traffic resources, each GPRS user makes        multiple access attempts to the system;    -   an average queue waiting time (for one GPRS user) expressed as a        function of the time necessary for the mobile terminal to make        the multiple access attempts to the system;    -   that the entire message is deemed to have been put in the queue;    -   an inter-arrival time between the data calls (arrivals process)        having exponential distribution with parameter λ equal to the        frequency of the arrivals;

an average call duration (service time τ) having exponentialdistribution with parameter μ=1/τ equal to the call death intensity;

-   -   an average waiting time in the queue having exponential        distribution with parameter a equal to the frequency of the        dropped calls (user “impatience”).

As far as the characteristics of the GPRS data service are concerned,the known method takes into account that:

-   -   each user (or, rather, each GPRS mobile terminal) attempts to        access the system, in accordance with various policies, for a        predetermined number of seconds with multiple attempts; if the        user has been unable to access the radio slot at the end of this        time period, the call is blocked;    -   access to the radio slot in the system is gained, in a known        manner, on a call basis and not for the individual message        packet;    -   the transmission speed of the message, after obtaining the radio        resource, depends on the number of users multiplexed on the GSM        time slot; this number goes, for example, from a minimum of one        user to a maximum of eight; as a consequence of this, the speed,        as is known, can vary during transmission of the single message        on the basis of the number of users who access the GSM-GPRS        cell.

According to the known method the data traffic “A” offered to the cellis evaluated by means of the following relation:$A = {\frac{\lambda}{\mu} = {\lambda \cdot \tau}}$where: $\tau = {\frac{nL}{v_{canal}} = \frac{1}{\mu}}$minimum service time of a data call;andv_(canal) speed of the single server;n·L length of the message (n packets of length L).

By knowing the number of slots available at any moment for the GPRSservice, the set of possible status associated with a cell is thensummed up in flow balancing equations required for calculating thevarious status probabilities, given by the relation:$P_{x} = {P_{0}\frac{\lambda_{0}\lambda_{1}\quad\ldots\quad\lambda_{x - 1}}{\mu_{1}\mu_{2}\quad\ldots\quad\mu_{x}}}$where P₀ is the probability of the system being in status 0; the set ofprobabilities is then normalised by means of the P₀ normalisationrelation, corresponding to the formula:$P_{0} = {\left( {1 + {\sum\limits_{k = 1}^{\infty}{\prod\limits_{i = 0}^{k - 1}\quad\frac{\lambda_{i}}{\mu_{i + 1}}}}} \right)^{- 1}.}$

In the known system, the voice traffic has priority over the GPRS datacalls (preemption) and it is necessary to weigh up the various possibleconfigurations of slots available for the data service with theprobability, linked to voice traffic only, of each configurationeffectively occurring. For this purpose, the state of the art makes itpossible to assess the probabilities of having x channels or slots leftfree by voice, and therefore usable by the GPRS service, through therelation: $\left\{ \begin{matrix}{{P^{D}(x)} = {P^{V}\left( {C - x} \right)}} & {1 \leq x < D} \\{{P^{D}(D)} = {\sum\limits_{i = 0}^{C - D}{P^{V}(i)}}} & \quad\end{matrix}\quad \right.$where C represents the number of channels of a cell, D corresponds tothe maximum number of channels allocable for data (static plus dynamic)and P^(V)(i) is the probability of having “i” channels occupied byvoice, given by the relation of a known kind:${P^{V}(i)} = {\frac{\frac{\left( A_{voice} \right)^{i}}{i!}}{\sum\limits_{j = 0}^{C - 1}\frac{\left( A_{voice} \right)^{j}}{j!}}.}$where A_(voice) represents the voice traffic offered to the cell.

The effective performance of the cell (probability of data block anduser throughput) is therefore given by the following relations:$B_{D} = {\sum\limits_{x = 1}^{D}{{B(x)} \cdot {P^{D}(x)}}}$average probability of data block;$R_{D} = {\sum\limits_{x = 1}^{D}{{{ET}(x)} \cdot {P^{D}(x)}}}$average data delay;where B(x) and ET(x) are the average data loss probability and theaverage delay associated to the configuration with “x” channelsavailable for data traffic.The user throughput is calculated on the basis of the average delay, bymeans of the relation (of known type): $\frac{n \cdot L}{R_{D}}$with message length n·L,

In the specific case of the GSM-GPRS network, data traffic for thevarious types of service is managed (served) using radio carriers ofpredefined frequency and, in the framework of each radio carrier (FDMAaccess technique), by a given slot (the logic channel) among thoseperiodically available in the framework of the time frame used on theradio interface (TDMA access technique). In this context, if even oneuser requests a data transmission, one or more whole slots of the GSMtime frame are assigned to the user as a function of the terminalcapability (preferred number of time slots requested to the network) ofthe mobile station; this implies a given transmission speed, for example9.05 kbit/s nominal per slot, for the data encoding denominated CS-1, or13.4 kbit/s nominal per slot for the date encoding denominated CS-2.

If, on the other hand, several users simultaneously request datatransmission, one or more slots are subdivided among the usersthemselves, with a consequent drop in the transmission speed which willtherefore be a function of the number of active users in the system(cell) at that moment; in a more intuitive manner, the generic usernotes a net data transmission speed which varies with time on the basisof the load conditions in the system.

In other words, the known method for determining the call deathprobability associated to a determined network status is based onconsidering that each terminal on the cell uses a same capability.

From Applicant's analysis of the known method, it emerges that themethodology for assessing dimensioning and performance of the basestations of a network for mobile telecommunications apparatuses isinadequate.

In fact, a cell of a real network comprises data terminals requestingdifferent numbers of time slots to the network for transferring data.

DISCLOSURE OF THE INVENTION

Object of this invention is the implementation of a method for assessingthe dimensioning and performance of base stations in a network formobile telecommunications apparatuses which does not have the limitdescribed in the known state of the art and which takes into account thecoexistence of data calls associated to different terminals havingdifferent capabilities or preferred number of time slots requested tothe network.

This object is achieved by the method as described in the claims.

In particular, object of present invention is a method for determiningcall death probabilities associated to a determined status of a networkcell when the network comprises data terminals having different terminalcapabilities.

Moreover, object of present invention is a computer program productloadable into internal memory of computers for implementing the methodof the invention as well as the network dimensioned by using the methodof the invention.

BRIEF DESCRIPTION OF DRAWINGS

This and the other features of this invention will be clear from thefollowing description of a preferred form of embodiment, provided forexemplificative and not limitative purposes, with the aid of theattached drawings, in which:

FIG. 1 shows a diagram of the inputs needed for applying the method forassessing the characteristics of a base station for mobiletelecommunications apparatuses, according to the invention, and theoutputs guaranteed by the method itself;

FIG. 2 is a flow diagram of the method according to the invention; and

FIG. 3 is a description of a possible status of a cell of the GSM-GPRStype (in terms of the frequency of births and deaths of data callsprovoking exit from the state itself) when the number of users for datatraffic (GPRS users) in the system is not higher than the maximumpermitted and when the number of GPRS users, present in the cell, issuch as to require a part of the calls to be put in the queue.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to FIG. 1, a method 10 for assessing the characteristicsin terms of dimensioning and performance of a mobile telecommunicationsnetwork, for example a GSM-GPRS mobile telecommunications network,envisages a set of inputs composed, in detail, of performance requiredfor the voice traffic (voice loss) 20, of performance required for thedata traffics (data loss or user throughput for each traffic streamcharacterised by a different terminal capability) 30, of descriptions ofthe offered voice traffic (Erlang) 40 and of descriptions of the offereddata traffic (GPRS traffic) 50 composed of the call arrival frequencyand terminal capability of the data calls for each traffic stream andaverage length of the individual message.

The method 10, according to the invention, is suitable for supplyingboth an optimal dimensioning 60 of the GSM-GRPS cell (number of radiocarriers) given the required performance 20 and 30, and the trafficoffered, 40 and 50, and the effective performance 70 of the cell itselfgiven the inputs 20, 30, 40 and 50.

In particular, from the operative point of view, the method 10 forassessing the dimensioning and performance of a base station in a mobiletelecommunications network suitable for managing voice and data, aGSM-GPRS network for example, comprises a set of stages which can begrouped in six fundamental logical blocks.

A first block 10000 (FIG. 2), of known type, suitable for assessing thenumber of traffic channels (slots) required (step 150) on the basis ofthe voice traffic to handle or Erlang 40 offered to the cell (step 100)and under the constraint of guaranteeing a voice loss not greater thanthe voice loss 20 required for voice only (step 200).

A second block 20000, of known type, suitable for assessing the minimumnumber of radio carriers to allocate in the cell (step 350), on thebasis of the number of signalling channels necessary (step 300),deducible, in a known manner, from the number of channels calculated instep 150 of the first block 10000, and on the basis of the number ofchannels (step 400) statically reserved for data traffic (50) only.

A third block 30000, as will be described in greater detail below,suitable for assessing the performance of the data traffic, in thesection between the mobile terminal and the base station or uplinksection (step 550), on the basis of

-   -   number of radio carriers available obtained with step 350 of the        second block 20000;    -   offered data traffic characteristics having different        -   data call arrival frequency,        -   terminal capability,        -   length of the packet,        -   average number of packets per message (step 500), for each            data traffic stream associated to a determined terminal            capability;    -   required performances of a data cell, i.e.        -   average data call loss (step 600), and        -   average delay (step 700);    -   maximum numbers of channels allocable dynamically to the data        services (step 800);    -   parameters indicating the maximum length of waiting time in the        queue of a data call (step 900); and    -   codification used for data transmission (step 1000), for example        parameters relating to the type of GPRS encoding used.

A fourth block 40000, substantially for assessing the results obtained,suitable for confirming, increasing or reducing the number of radiocarriers used by the third block 30000, comprising a first control stepfor controlling if the performance satisfies the dimensioningrequirements (step 1100).

If the outcome is positive, this step 1100 completes the block 40000and, if the outcome is negative, it leads to a second control step forcontrolling if an improvement has been obtained in the step 30000 in thecell performances compared with any previous situation (step 1200).

In the event of a negative outcome, this step 1200 leads to a step (step1250) suitable for returning the number of channels to those used inblock 30000 representative of a previous situation, and in the case of apositive outcome it leads to an increase in the number of channels (step1150), if possible, knowing the maximum number of carriers allocable ina GSM cell, and to repetition of block 30000.

A fifth block 50000 for assessing the performance of the data trafficsin the section between the base station and the mobile terminal ordown-link section (step 1350), on the basis of the number of radiocarriers available (confirmed or calculated in blocks 30000 and 40000),on the basis of the set of inputs relating to the data traffic offered(step 1300) as described for steps 500, 600 and 700 of the block 30000and on the basis of the set of configuration parameters (step 1400) asdescribed in steps 800,900 and 1000 of block 30000.

A sixth block 60000 substantially for assessing the results obtained,suitable for confirming, increasing or reducing the number of radiocarriers used by the fifth block 50000; this block 60000 issubstantially equivalent to block 40000, already described, andcomprises steps 2100, 2200, 2250 and 2150 respectively equivalent tosteps 1100, 1200, 1250 and 1150 already described.

Knowing the maximum number of carriers allocable in a cell of mobileapparatuses, of the GSM type for example, block 60000 leads tocompletion of method 10, according to the invention, recycling on block50000 where applicable.

In the method according to the invention, the first two blocks 10000 and20000 will only be described in broad lines, just like blocks 40000 and60000; blocks 30000 and 50000, on the other hand, include innovativecomponents due to the different data traffic characteristics consideredwith respect to the state of the art and will be described in detail.

The functions carried out by the various blocks are implemented, inaccordance with the object of this invention, in the form of programs ona computer and make it possible to determine the characteristics of anetwork for mobile telecommunications apparatuses.

The operation of method 10 for assessing the dimensioning andperformance of a cell in a mobile telecommunications system is describedtaking a network of the GSM-GPRS type as reference, even though it canbe understood by technicians in the sector that the method 10 is easy toextend to mobile networks suitable for managing data traffic and/orvoice and data traffic.

In particular, the dimensioning as described can be advantageouslyapplied to networks of type TDMA and FDMA/TDMA.

The first block 10000 makes it possible to assess the minimum number oftraffic channels (slots) required (step 150) to handle the voice trafficoffered (Erlang) to the cell (step 100), under the constraint ofguaranteeing a voice loss not greater than the voice loss required forvoice only (step 200).

For this purpose, step 150 of block 10000 uses the formula called“Erlang-B”, known as such (model M/M/N) in first and second generationfixed and mobile telecommunications networks which, on the basis ofknown input data, provides the number of traffic channels to allocate inthe GSM-GPRS cell to handle the traffic expressed in Erlang with therequested performance (voice drop-out).

The second block 20000 makes it possible to assess the number of radiocarriers (FDMA access technique) to allocate in the cell, assuming thefollowing as known:

-   -   the total number of traffic channel (TDMA access technique)        associated with each radio carrier which, as is known, is eight        channels in the case of the GSM system;    -   the rule of association, known as such, between the number of        traffic channels calculated by the first block 10000 and the        number of signalling channels needed for managing the cell (step        300);    -   the number of channels allocated statically to the GPRS traffic,        and therefore not usable in any case by voice traffic (step        400); in general this is a design parameter.

In accordance with this invention, the third block 30000 makes itpossible to assess the performance of data traffic (losses and userthroughputs) (step 550) in the uplink section on the basis of aplurality of input data, of characteristics of the GPRS data service andof assumptions regarding the method and model. In particular, as far asthe input data are concerned, step 550 takes into account:

-   -   the characteristics of the data traffics offered to the cell;        that is, for each data traffic stream, the call arrival        frequency, the terminal capability, the length of the packet and        the average number of packets per message (step 500);    -   the data call loss requested for each data traffic stream (step        600);    -   the user throughput requested for each data traffic stream (step        700);    -   the maximum number of channels dynamically allocable to the data        calls (step 800), that is, usable by the GPRS data traffics and        left free by the GSM voice traffic;    -   the maximum waiting time in the queue of a GPRS data call (step        900);    -   the GPRS encoding for transmission of the data (step 1000);    -   the number of carriers calculated by the second block 20000 in        step 350.

As far as the characteristics of the GPRS data service are concerned,block 30000 and the method take into account, for the purpose ofmodelling the behaviour of the GSM-GPRS cell for data traffic only (GPRStraffic):

-   -   an M/M/N/Q model in which the system servers correspond to the        cell traffic slots and the status of the cell is represented by        the vector m={m₁,m₂, . . . , m_(N)}, where the term m_(i)        represents the number of GPRS users in the system belonging to        the traffic stream i-th;    -   a queue of infinite length (Q=∞) in the case of congestion of        the traffic resources wherein each user makes multiple access        attempts;    -   an average queue waiting time (for one GPRS user) expressed as a        function of the time necessary for the mobile terminal to make        the multiple access attempts;    -   the entire message put in the queue;    -   an inter-arrival time, for traffic stream i-th, between the data        calls (arrivals process) characterised by exponential        distribution with parameter λ_(i) equal to the data call arrival        frequency (in this way, the description of the global arrivals        process associated to the complete set of traffic streams is        given by the vector λ={λ₁,λ₂, . . . , λ_(N)});    -   an average call duration (service time τ) characterised by        exponential distribution with parameter μ=1/τ equal to the call        death intensity;    -   an average waiting time in the queue characterised by        exponential distribution with parameter α equal to the frequency        of the dropped calls (user “impatience”).

On the basis of what has been listed, block 30000 makes it possible toassess the vector of data traffics A={A₁,A₂, . . . , A_(N)} offered tothe cell by means of the following relations:$A_{i} = {\frac{\lambda_{i}}{\mu} = {\lambda_{i} \cdot \tau}}$for traffic stream i-th;where: $\tau = {\frac{n\quad L}{v_{canal}} = \frac{1}{\mu}}$minimum service time of a data call;andv_(canal) speed of the single server;n·L length of the message (n packets of length L).

According to a feature of present invention, the performance of the cellon the uplink section (probabilities of data block and average userthroughputs) are assessed using modelling of the cell status based ontwo different types of “cell status” characterised by the presence of Ndifferent data traffic streams.

If m={m₁,m₂, . . . , m_(N)} is the vector of GPRS users in the system,we get:

-   -   the status 110000 (FIG. 3, FIG. 2) concerning a two-dimension        case for a simpler explanation, in which the number of GPRS        users in the system (described by vector m={m₁,m₂}) does not        exceed the maximum number of data connections simultaneously        supportable by the cell, where the number of slots available in        a given moment for the data service is known; in this case the        system exits the state “m₁,m₂” because of the birth of a new        data call (with data call arrival frequencies λ₁ and λ₂) or        because of the death of a call in progress; the global frequency        of the death is k·μ, where k is the number of GSM slots occupied        by one or more GPRS users.    -   The frequency of the death associated to each traffic stream is        evaluated by means of a repartition of the global frequency of        the data call death.    -   According to present invention, a set of models is defined for        permitting to evaluate in a simple and fast way the medium        frequency of the death related to each single traffic stream;        this medium frequency, according to present embodiment, depends        on the following parameters:    -   m₁ number of users belonging to data traffic stream 1;    -   m₂ number of users belonging to data traffic stream 2;    -   C₁ terminal capability associated to data traffic stream 1;    -   C₂ terminal capability associated to data traffic stream 2;    -   N number of slots available for data traffics;    -   k number of slot occupied by data traffics;    -   M_(max) maximum number of users multiplexed on a time slot;    -   and it also depends on the following conditions:        -   if m₁·C₁+m₂·C₂≦N        -   then            -   a′(m₁,m₂)=m₁·C₁            -   b′(m₁,m₂)=m₂·C₂            -   a′(m₁,m₂)+b′(m₁,m₂)=k        -   if            -   m₁·C₁+m₂·C₂>N            -   m₁·C₁+m₂·C₂≦N·M_(max)        -   then            ${a^{\prime}\left( {m_{1},m_{2}} \right)} = {\frac{m_{1} \cdot C_{1}}{{m_{1} \cdot C_{1}} + {m_{2} \cdot C_{2}}} \cdot N}$            ${b^{\prime}\left( {m_{1},m_{2}} \right)} = {\frac{m_{2} \cdot C_{2}}{{m_{1} \cdot C_{1}} + {m_{2} \cdot C_{2}}} \cdot N}$        -   defined        -   C_(R) as the reduced terminal capability (reduced number of            used time slots respect to preferred number of time slots            requested to the network) associated to data traffic stream            1 or 2;    -    and under the hypothesis that only one user accesses the system        with a reduced terminal capability (the last user accessing the        system before the filling up of the queue)        -   if            -   m₁·C₁+m₂·C₂>N·M_(max)            -   m₁·C₁+m₂·C<N·M_(max)+min(C₁,C₂)        -   then            ${a^{\prime}\left( {m_{1},m_{2}} \right)} = {\frac{m_{1} \cdot C_{1}}{{m_{1} \cdot C_{1}} + {\left( {m_{2} - 1} \right) \cdot C_{2}} + {1 \cdot C_{R}}} \cdot N}$            ${b^{\prime}\left( {m_{1},m_{2}} \right)} = {\frac{{\left( {m_{2} - 1} \right) \cdot C_{2}} + {1 \cdot C_{R}}}{{m_{1} \cdot C_{1}} + {\left( {m_{2} - 1} \right) \cdot C_{2}} + {1 \cdot C_{R}}} \cdot N}$    -    in the example above the reduced terminal capability regards        the data traffic stream 2 but can concern also data traffic        stream 1 if the last user accessing the system belongs to the        first traffic; in that case the above models have to be modified        considering the reduced terminal capability associated to data        traffic stream 1;        -   if            -   m₁·C₁+m₂C₂≧N·M_(max)+min(C₁,C₂);            -   m₁·C₁+m₂·C₂<N·M_(max)+max(C₁,C₂)            -   C₂>C₁        -   then            ${a^{\prime}\left( {m_{1},m_{2}} \right)} = {\frac{m_{1} \cdot C_{1}}{{m_{1} \cdot C_{1}} + {\left( {m_{2} - 1} \right) \cdot C_{2}} + {1 \cdot C_{R}}} \cdot N}$            ${b^{\prime}\left( {m_{1},m_{2}} \right)} = {\frac{{\left( {m_{2} - 1} \right) \cdot C_{2}} + {1 \cdot C_{R}}}{{m_{1} \cdot C_{1}} + {\left( {m_{2} - 1} \right) \cdot C_{2}} + {1 \cdot C_{R}}} \cdot N}$    -    the same reduced terminal capability can regard the data        traffic stream 1 under the opposite condition C₁>C₂; in that        case the above models have to be modified considering the        reduced terminal capability associated to the first traffic.    -   the status 210000, in which the number of GPRS users in the        system (described by vector m={m₁,m₂}) exceeds the maximum        number of data connections simultaneously supportable by the        cell, where the number of slots available in a given moment for        the data service is known; in this case the system exits the        state “m₁,m₂” because of the birth of a new data call (with data        call arrival frequencies λ₁ and λ₂) or because of the death of a        call in the systems as a result of two causes:        -   the completion of a call in progress which occurs with death            global frequency equal to N·μ, where N is the maximum number            of slots usable by the data service;        -   the departure of a data call from the queue as a result of            termination of the waiting time envisaged by the system            which occurs with a death global frequency equal to N_(Q)·α,            where N_(Q)=m₁+m₂−c(m₁,m₂) corresponds to the total number            of GPRS users (belonging to data traffic streams 1 and 2) in            the queue who each contribute with an additional term equal            to α.    -   Also in this case, the frequency of the death associated to each        traffic stream is evaluated by means of a repartition of the        global frequency of the data call death.    -   In particular, according to present embodiment, it is convenient        to evaluate each frequency of the death a″ and b″ starting from        the frequency of the death given by N·μ for the connected users        and, in addition, the frequency of the death a′″ and b′″        starting from the frequency of the death given by N_(Q)·α for        the queued users.    -   In this context, according to present invention, an improvement        is not only the use of the set of models described for the state        110000 but also the definition of a fast and efficient algorithm        devoted to the evaluation of SQ possible sequences of users        accessing the system for the state m={m₁,m₂}; to each sequence        it is associated a specific repartition of the frequencies of        the death N·μ and N_(Q)·α.    -   The model described below permits to build in a very simple way        S sets of sequences or “configurations” characterised in that        the sequences belonging to a single set have the same        repartition of the frequency of the death and each of the S sets        of sequences has a different repartition of the frequency of the        death.    -   In particular, according to present embodiment, for each set it        is considered only one configuration as representative of all        the possible permutations having the same repartition of the        frequency of the death.    -   In this way it is possible to reduce in a huge way the amount of        elaborations and to calculate only the S<<SQ different        configurations.    -   As consequence of this, the frequency of the death associated to        each data traffic stream depends on the following parameters:    -   m₁ number of users belonging to data traffic stream 1;    -   m₂ number of users belonging to data traffic stream 2;    -   C₁ terminal capability associated to data traffic stream 1;    -   C₂ terminal capability associated to data traffic stream 2;    -   N number of slots available for data traffics;    -   M_(max) maximum number of users multiplexed on a time slot.    -   Given the vector m={m₁,m₂}, the components of the frequency of        the death associated to each traffic stream can be evaluated as        follows:    -   1. it is built the “configuration j” of access to the cell in        which before enter the system users characterised by the smaller        terminal capability (in the example is C₁<C₂)        -   C₁C₁C₁C₁ . . . C₁C₂C₂C₂C₂ . . . C₂        -   ______m₁______ . . . ______m₂______    -   2. it is evaluated the “access cut” in which the capacity of the        cell (given by the formula N·M_(max)) is completely occupied        -   C₁C₁C₁|C₁ . . . C₁C₂C₂C₂C₂ . . . C₂        -   ______m₁______ . . . ______m₂______    -   3. it is calculated (using a set of binomial formulae) the        number of possible “permutations”, with the individuated “access        cut”, obtainable considering the vector m={m₁,m₂} of users        characterising the status;    -   4. the two different components of frequency of the death        associated to each data traffic stream are calculated for the        “configuration j”:        -   for users connected to the N available time slots, the            models described for state 110000 are applied to the set of            users placed to the left of the “access cut”; in this way            the terms a_(j)″(m₁,m₂;) and b_(j)″(m₁,m₂) are obtained;    -   for users placed in the queue, it is calculated the repartition        between the data traffic streams 1 and 2 and the terms        a_(j)′″(m₁,m₂) and b_(j)′″(m₁,m₂) are evaluated;    -    it is obvious that all “permutations” associated to the        “configuration j” are characterised by the same frequencies of        the death given by the set a_(j)″,a_(j)′″,b_(j)″,b_(j)′″;    -   5. it is built a new sequence or “configuration” inverting the        position of two users belonging the first one to the data        traffic stream 1 and the second one to the data traffic stream 2        -   C₁C₁C₁C₁ . . . C₂C₁C₂C₂C₂ . . . C₂        -   ______m₁______ . . . ______m₂______    -    the step 2 is repeated; if the new “access cut” is different        from the previous also steps 3 and 4 are repeated and other        “permutations”, and therefore frequencies of the death, are        calculated; if the new “access cut” is equal to the previous,        step 5 is repeated until a new different “access cut” is        obtained; the process based on steps 1, 2, 3, 4 and 5 is stopped        when is obtained the “access cut” composed by users belonging to        data traffic stream 2 only.    -   At the end of the process based on steps 1, 2, 3, 4 and 5, a        certain number of “configurations” and a great number of        “permutations” “i” are known in terms of components        a_(i)″,a_(i)′″,b_(i)″,b_(i)′″; the total components        a″,a′″,b′,b′″ are calculated as average of sets        a_(i)″,a_(i)′″,b_(i)″,b_(i)′″ associated to the permutations        evaluated.

In presence of N different data traffic streams the existence ofpossible infinite status due to a queue of infinite length, conducts toa further improvement of the method for limiting the number of status inorder to calculate in an efficient way the set of status probabilities,as described below.

When N data traffic streams are offered to a multi-dimensional systemcharacterised by an infinite queue, the evaluation of the set of statusprobabilities requests the building and resolution of a N-dimensionalmatrix with an infinite number of elements.

According to present invention it is provided a method for evaluatingthe maximum number of users M_(i) ^(max), associated to stream i-th,accessed in the system; this parameter is evaluated taking into accountonly stream i-th and offering its traffic to a mono-dimensional system;in this way M_(i) ^(max) is obtained identifying the state “j” in whichthe state probability P_(j) becomes negligible (that is, very small).

In other words each of the traffic streams offered by terminals having adetermined terminal capability is separately analysed (mono-dimensionalevaluation).

This approach is considered adequate to limit the dimension of theproblem and to guarantee an efficient time of elaboration.

Knowing all the frequencies of the death it is possible to build Qmatrix that is a square “sparse matrix” with dimension (M₁ ^(max)·M₂^(max)· . . . ·M_(N) ^(max)).

Knowing the number of slots available at any moment for the GPRSservice, the set of possible status probabilities associated to a cellis given by the relation: $\quad\left\{ \begin{matrix}{{\overset{\_}{\pi} \cdot Q} = 0} \\{{\sum\limits_{i = 1}^{M_{1}^{\max}}{\sum\limits_{j = 1}^{M_{2}^{\max}}{\cdots{\sum\limits_{k = 1}^{M_{N}^{\max}}\pi_{1,{j\ldots}\quad,k}}}}} = 1}\end{matrix} \right.$where π_(i,j, . . . k) is the status probability of the system being ina status with i users belonging to data traffic stream l, j usersbelonging to stream 2 and k users belonging to the last stream;{overscore (π)} is the status probabilities vector. Therefore, thenumber of possible status and of associated status probabilities islimited in number as resulting from the indexes of the aboveexpressions.Due to that, Jacobi method, for example, can be used to solve thissystem and to obtain the normalised status probabilities; after theevaluation of this set of probabilities, data block probability B_(i)and data delay ET_(i) associated to each data traffic stream i-th andtotal data block probability B and total data delay ET are evaluated.

In summary, according to present invention, the cell dimensioning isdetermined on the basis of a set of status probabilitiesπ_(i,j, . . . k) associated to a set of cell status wherein each statusprobability is determined on the basis of arrival data call frequenciesand medium death frequencies of data calls associated to different typeof terminals.

In particular, the medium death frequencies of each cell status aredetermined by considering the S sequences having each a determinedrepartition of the global frequency of the death.

What has been described so far, and underlined several times, must beintended as being associated with the number of slots available for thedata service at a given moment. As this number varies in real time onthe basis of the voice traffic which, in general, has priority over theGPRS calls, it is necessary to weigh up the various possibleconfigurations of slots available for the data service with theprobability, linked to voice traffic only, of each configurationeffectively occurring. For this purpose, block 30000 makes it possibleto assess the probabilities of having x channels left free by voice, andtherefore usable by the GPRS service, through the relation:$\quad\left\{ \begin{matrix}{{P^{D}(x)} = {{{P^{V}\left( {C - x} \right)}1} \leq x < D}} \\{{P^{D}(D)} = {\sum\limits_{i = 0}^{C - D}{P^{V}(i)}}}\end{matrix} \right.$where D corresponds to the maximum number of slots allocable for data(static plus dynamic) and P^(V)(i) is the probability of having “i”slots occupied by voice, given by the relation of a known kind:${P^{V}(i)} = \frac{\frac{\left( A_{voice} \right)^{I}}{i!}}{\sum\limits_{j = 0}^{C - 1}\frac{\left( A_{voice} \right)^{j}}{j!}}$where A_(voice) represents the voice traffic offered to the cell.

According to present invention, it is therefore possible to determinethe effective performance of the cell by the following relations:${Bi} = {\sum\limits_{x = 1}^{D}{{B_{i}(x)} \cdot {P^{D}(x)}}}$average probability of data block for data traffic stream i-th;${ET}_{i} = {\sum\limits_{x = 1}^{D}{{{ET}_{i}(x)} \cdot {P^{D}(x)}}}$average data delay of data traffic stream i-th;$B = {\sum\limits_{x = 1}^{D}{{B(x)} \cdot {P^{D}(x)}}}$average call data loss;${ET} = {\sum\limits_{x = 1}^{D}{{{ET}(x)} \cdot {P^{D}(x)}}}$average data delay;where B(x) and ET(x) are the average data loss probability and theaverage delay (associated to the entire set of data traffic streams)when “x” time slots are available for data service.User throughput is calculated in step 550 on the basis of the averagedelay, by means of the relation (of known type):$\frac{n \cdot L}{R_{D}}$with message length n·L.

Block 30000 comprises:

-   -   a method for calculating the medium death frequencies associated        to each typology of status of the cell as shown in FIG. 3;    -   a method for limiting the number of status of the cell; such a        method permits to apply, for example, the Jacobi method;    -   a method for determining the effective voice loss, data loss and        data user throughputs wherein the data performances are        determined by means of models which give data losses (total and        per stream) and average delays (total and per stream) on the        basis of the probability of having “x” slots available for data        traffics left free by voice calls.

The fourth block 40000 compares the quality of the performance assessedby the third block 30000 with the expected performance (call data lossand requested throughput) and decides the increase in the number ofcarriers in the cell (step 1150) if the performance is not met (step1100) and if:

-   -   the performance assessed is better compared with that obtained        in the previous step (step 1200) and, of course, the maximum        number of carriers allocable in a cell has not been reached.

Step 1100 makes it possible to avoid needless increase in the number ofcarriers if the performance, even if deemed unsatisfactory, cannot befurther improved (this can occur if the number of slots allocabledynamically to the data service, the GPRS service for example, is fixedand cannot be increased even when increasing the number of carriersassigned to the cell); the limit constituted by the maximum number ofcarriers available takes account of the limits of the spectral bands andthe rules which each mobile phone operator uses for carrying out radiodimensioning of the system base station.

The fifth block 50000, regarding the assessment of performance (datablock probability and user throughput associated to each data trafficstream) for the downlink section, has identical characteristics, fromthe point of view of the method and model assumptions, to block 30000regarding the opposite radio section (uplink section) and thereforereference should be made to that block.

The sixth block 60000 has identical characteristics to block 40000 andin this case too the description is omitted.

Obvious modifications or variations are possible to the abovedescription, in the dimensions, forms, materials, components, circuitryelements, connections and contacts, as in the details of the circuitryand construction-illustrated, and in the method of operating withoutstraying from the spirit of the invention as specified in the claimswhich follow.

1-7. (canceled)
 8. A method for dimensioning a cell of a mobiletelecommunications network suitable for managing data calls associatedto data terminals having different terminal capabilities, the cellcomprising a plurality of status, comprising: limiting the number ofsaid plurality of status associated to said cell accessed by a pluralityof different traffic streams associated to said data terminals;determining medium death frequencies of a single cell status byconsidering determined sequences of users accessing the cell and havinga different repartition of frequency of death; determining a global setof cell status probabilities of said cell on the basis of data callarrival frequencies and of the medium death frequencies of data calls;and dimensioning said cell on the basis of said global set.
 9. Themethod according to claim 8, wherein the step of limiting the number ofsaid plurality of status comprises the step of separately analysing eachtraffic stream of said plurality of traffic streams offered by said dataterminals.
 10. The method according to claim 8, wherein each of saiddetermined sequences has associated a set of sequences having the samerepartition of the frequency of the death.
 11. The method according tothe claim 8, wherein the network is a TDMA or TDMA/FDMA type network.12. The method according to claim 8, wherein the network is a GPRS typenetwork.
 13. A cell of a mobile telecommunications network suitable formanaging calls of different type data terminals, dimensioned by themethod of any one of claims 8 to
 12. 14. A computer program productdirectly loadable in the internal memory of at least a computer andincluding software code portions capable of performing the method of anyone of claims 8 to 12, when said product is capable of being run on atleast a computer.